Linearly expandable filament for electron gun structure



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LINEARLY EXPANDABLE FILAMENT FOR ELECTRQN GUN STRUCTURE Filed Jan. 7. 1963 INVENTOR.

ALFRED L. DONLEVY TMW ATTORNEYS United States Patent 3 286,117 LINEARLY EXPANDABLE FILAMENT FOR ELECTRON GUN STRUCTURE Alfred L. Donlevy, San Leandro, Calif., assignor to Stanffer Chemical Company, New York, N.Y., a corporation of Delaware Filed Jan. 7, 1963, Ser. No. 249,934 4 Claims. (Cl. 313-279) The present invention relates to electron gun structures wherein very high current electron beams are required such as, for example, in electron beam furnaces.

In many applications such as in electron beam melting and casting operations high current beams are employed necessitating high electron emission from a filament. Higher electron emission is achieved by running larger currents through a filament and extending the length of the filament. In employing both of these methods to increase the electron emission of the gun, the linear expansion of the filament becomes an increasingly more important factor in the design of the gun since any sagging of the filament may result in shorting of the filament and misalignment of the filament with respect to the other gun electrodes.

The principal object of this invention is to provide in an elongate filament electron gun provision for slidably mounting the filament within an elongate bore in a support whereby the filament is free to expand in a linear direction while, at the same time, the emission portion of the filament is supported in a substantially straight line.

One feature and advantage of this invention lies in the fact that as the filament heats up and freely expands linearly the outward edges of the bore through the filament support provides a lever action to support the length of the filament in a substantially straight path.

Another object of this invention is to provide in such an electron gun filament support each of which has a bore therein with a diameter only slightly larger than that of the filament and a length many times the filament diameter. In such a gun structure a long length of the filament can be supported in a substantially straight path by the filament supports.

Other objects of the present invention will become apparent on reading the following specification and referring to the accompanying drawing in which similar characters of reference represent corresponding parts in each of the several views.

In the drawing:

FIG. 1 is a perspective view of an electron gun in accordance with this invention;

FIG. 2 is an enlarged side view, partly in section, of the filament structure shown in FIG. 1 taken along line 2-2 1n the direction of the arrows; and

FIG. 3 is a side view of another embodiment of the present invention.

Referring now to the drawing and with particular reference to FIGS. 1 and 2 there is provided an electron gun including a backing electrode 11 defining a generally cylindrical emission chamber 12 therein. This chamber communicates with the exterior of the backing member at a relatively large opening longitudinally of the electrode 11 and chamber 12. Immediately above a lower lip 13 of the backing electrode 11 and within the chamber 12 adjacent the longitudinal opening thereof, there is disposed a filament 14 comprising first and second parallel emitters 15 and 16. The emitters 15 and 16 of the filament may, for example, be formed of tungsten wire and are joined together at one end thereof to thereby form a U-shaped configuration, as illustrated.

These two emitters 15 and 16 are supported in closely spaced parallelism by means of a filament support block at each end thereof. As illustrated, at the U-shaped end ice of the filament 14 the first and second emitters 15 and 16 are supported within bores in blocks 17 and 18, respectively, and at the other end of the filament within bores in blocks 19 and 20, respectively. At each end of the filaments 15 and 16 the separate support blocks are mounted together and on the backing electrode 11 by means of insulators 21.

Externally of the backing electrode 11 there is disposed an electron accelerating electrode 22 which extends longitudinally thereof with a leading edge of the accelerating electrode adjacent and below the lower lip 13 of the backing electrode 11. Thermionic emission from the filament 14 is accomplished by energization of this filament, such as illustrated schematically by the power supply 23 connected across the free ends of the emitters 15 and 16. An electrostatic accelerating field is established by energization of the accelerating electrode 22, and this is schematically illustrated by a battery 24 having its positive side electrically connected to the accelerating electrode and the negative side thereof returned to the backing electrode and the filament as through ground connections. Electrons thermionically emitted from the emitters 15 and 16 are acted upon by the accelerating electrostatic field established between the accelerating electrode 22 and the filament and backing electrode so as to be attracted away from the filament.

As shown in FIG. 2 the elongate bores 17a, 18a, 19a and 20a in the filament support blocks 17, 18, 19 and 20, respectively, in which the filament is slidably supported have a diameter only slightly larger than that of the filament 14 whereby as the filament heats up due to current" passing therethrough it will expand linearly an appreciable amount and slide through these bores in block 17-20. The blocks 17-20 are preferably of the same material or a material having the same or greater coefficient of expansion as the filament 14.

The portions of the blocks 17-20 at the outward edges of the bores 17a-20a therethrough provide a lever action as illustrated to support the unsupported length of the filament and maintain the filament in a substantially straight path.

The blocks have a length which is many times the diameter of the filament passing therethrough, preferably being more than three times the filament diameter.

Also, the blocks effectively serve to define the limits of tle emission portion of the filament for defining the beam e ges.

It has been discovered in a typical electron gun according to the present invention that a pair of tungsten filaments 0.070 inch in diameter, 4 inches long, and spaced apart by a distance 0.250 inch can be supported at their opposite ends by filament support blocks which have a bore therethrough 0.250 inch long and 0.073 inch in diameter.

Referring now to FIG. 3 there is shown an alternative embodiment of this invention where an elongate filament 25 is rigidly supported at one end thereof on a metallic support post 25 and slidably supported at the other end thereof in a bore through a support block 27 of the type described with reference to FIGS. 1 and 2. The support block 27 is mounted on an insulator 28 and current is applied to the filament 25 by a lead (not shown) connected to the support post 26 and a lead 29 connected to the end of the filament 25 projecting through the block 27. In this embodiment although the filament 25 is fixedly secured at one end it is free to slide through the support block 27 at the other end as the filament expands.

While the structure of FIG. 3 slidably supports an elon gate filament by a lever action at one end thereof, the structure according to FIGS. 1 and 2 slidably supports the filament by a lever action at both ends, whereby the center of the filament will not be caused to move during filament expansion.

While these and other details have been shown by way of illustration and example for the purpose of clarity and understanding, it is understood that certain changes and modifications can be made within the spirit of the invention as limited by the scope of the attendant claims.

What is claimed:

1. in an electron gun the combination of a gun housing, an elongate cathode filament having a straight line portion and support means for supporting said elongate filament in said housing, said support means including at least one support block positioned adjacent said straight line portion of said filament, said support block being provided with a bore therethrough having a diameter only slightly larger than the diameter of said filament and providing a lever action on said filament to support the straight line length of said filament while permitting said filament to slide therethrough.

2. In an electron gun the combination of a gun housing, an elongate cathode filament having a straight line portion and support means for supporting said elongate filament in said housing, said support means including at least one support block positioned adjacent said straight line portion of said filament, said support block being provided with a bore therethrough having a diameter only slightly larger than the diameter of said filament and a length many times the bore diameter, said support block providing a lever action on said filament to support the straight line length of said filament while permitting said filament to slide therethrough.

3. In an electron gun a gun housing, an elongate cathode filament and support means for slidably supporting said filament in spaced relation with respect to said housing with at least a portion of said filament supported in a substantially straight line, said support means ineluding at least one support block at each end of said straight line portion of said filament, each of said support blocks provided with a bore therethrough in line with the bore of the other block and the straight line portion of said filament, said bore constructed and arranged to slidably support said filament therein and provide a lever action on said filament to maintain said filament in the straight line between said support blocks.

4. In an electron gun a gun housing an elongate cathode filament having a substantially straight line portion and support means for supporting said filament in spaced relation with respect to said gun housing, said support means including at least one support 'block at each end of the straight line portion of said filament, each of said support blocks provided with a bore therethrough in line with the bore of the other block and said straight line portion of said filament and having a diameter slightly larger than the diameter of said filament and a length many times the diameter of said filament for providing a lever action on said filament, whereby during expansion said filament slides through said support blocks while maintaining the straight line position.

References Cited by the Examiner UNITED STATES PATENTS 2,783,353 2/1957 Finn 219-536 2,877,417 3/1959 Senior 2l9-536 3,140,417 7/1964 Tietze 313279 FOREIGN PATENTS 906,264 9/ 1962 Great Britain.

JOHN W. HUCKERT, Primary Examiner.

R. F. POLLISSACK, Assistant Examiner. 

1. IN AN ELECTRON GUN THE COMBINATION OF A GUN HOUSING AN ELONGATE CATHODE FILAMENT HAVING A STRIAIGHT LINE POR TION AND SUPPORT MEANS FOR SUPPORTING SAID ELONGATE FILA MENT IN SAID HOUSING, SAID SUPPORT BLOCK POSITIONED ADJACENT SAID LEAST ONE SUPPORT BLOCK POSITINED ADJACENT SAID STRAIGHT LINE PORTION OF SAID FILAMENT, SAID SUPPORT BLOCK BEING PROVIDED WITH A BOFE THERETHROUGH HAVING A DIAMETER ONLY SLIGHTLY LARGER THAN THE DIAMETER OF SAID FILAMENT AND PROVIDING A LEVER ACTION ON SAID FILAMENT TO SUPPORT THE STRAIGHT LINE LENGTH OF SAID FILAMENT WHILE PEMITTING SAID FILAMENT TO SLIDE THRERTHTOUGH. 